The promise of modern society has been resolving problems by scientific explanations and predicting future developments based on well grounded scientific knowledge. Instead contemporary society is confronted with growing uncertainty in scientific knowledge and a variety of risks and vulnerabilities especially in environmental management and decision making. In the last decade an intense discussion of the limits of scientific knowledge and the growing importance of ignorance was started within research fields of Sociology of Science and the Sociology of Scientific Ignorance (SSI). One of the main arguments is, that it has to be acknowledged, that science often can not provide sufficient knowledge in the moment of decision making. Consequently decision making based on well grounded scientific knowledge in reality can hardly be achieved and often decisions will be based on incomplete scientific knowledge. Against this background the crucial question emerges: How decision making in face of ignorance is possible? Sociologists claim that the society has to be prepared for dealing with well defined ignorance – especially by changing the focus from knowledge to nonknowledge. It is assumed, that a more open attitude towards ignorance and its acknowledgement leads to new areas of action and better decision making. To date it is rarely specified how such a swift could look like. The analyze of case studies shows, that in certain cases actors develop strategies to deal successful with incomplete knowledge – they take into account ignorance in decision making. This PhD work is carried out within the frame of an interdisciplinary research program on revitalization of large scale contaminated areas and its revitalization. In all industrialized countries during the last century human activities such as industries, mining and military have lead to contaminations in soil and groundwater. Such contaminations pose a risk for human health and ecosystem functions. Due to the long history of contaminations knowledge on former dumps has often been lost and natural degradation processes transformed original contaminants. For this reasons decision making in revitalization projects has to permanently deal with (known) unknowns and actors have to decide in spite of ignorance. Within the PhD thesis governance and communication structure of decision making in face of ignorance will be analyzed. Central questions of the work are: How ignorance and non-knowledge can be taken into account in decisions? How actors do agree upon what is not known? Which influence has the professional background of each actor on handling with ignorance? How decision making in spite of uncertainty and potential risks is possible, which strategies and organizational arrangements can be found to deal successfully with uncertainty, ignorance and unforeseen outcomes? The work is focused on negotiation and organization of revitalization projects. For this reason a case study has been chose – a revitalization project in an old industrialized area – where decisions and critical points shall be analyzed with regard to ignorance. Methodologically the work will be based on narrative interviews with actors of the respective project but also with experts in revitalization and cleaning up of contaminated areas. Additional information was taken from working meetings and political discussions on local but also on regional level. The transcribed interviews as well as the other materials (minutes etc.) were codified with the Maxqda-software for qualitative data analyze. Based on the approach of Grounded Theory the analysis will be conducted. The result of the work shall contribute to the theoretical discussion in the field of sociology of ignorance and should also give practical advices for decision making in face of ignorance in environmental management.